1. Field of the Invention
The present invention relates to a high withstand voltage diode and a method for manufacturing such a high withstand voltage diode, and more particularly to a high withstand voltage diode suitable for use in protection of a high-voltage transistor, such as diode having a withstand voltage of 60 to 300 V which is used in the protection of a driver IC for a plasma display panel, or a protective diode having a withstand voltage of 200 to 1000 V in the protection of a power supply IC, and to a method for manufacturing such a diode.
2. Background of the Invention
Prior art related to the present invention will be described with regard to the example of a 150-V diode that is fabricated on a p-type semiconductor substrate, such as shown in FIG. 4(a).
This high withstand voltage diode is fabricated by forming an n-type diffusion layer 32 having a surface concentration of 1xc3x971016 atoms/cm3 and a depth of approximately 15 xcexcm as a cathode on a 1xc3x971014 atoms/cm3 substrate, and forming a p-type diffusion layer 34 onto that surface as an anode, and forming a n-type high-concentration diffusion layer 35 that serves as the cathode, which is approximately 15 xcexcm distant from the anode. To alleviate the electrical field in the area surrounding the high-concentration p-type diffusion layer 34 of the anode, a low-concentration p-type diffusion layer 33 is formed.
The reference numeral 38 denotes a cathode electrode that is formed on the high-concentration n-type diffusion layer 35, 39 is an anode electrode that is formed on the high-concentration p-type diffusion layer 34, and 36 is a field insulation layer.
When the above-noted high withstand voltage diode is used for protecting a high-voltage transistor, however, because it is necessary to set the withstand voltage of the diode to a voltage that is lower than the withstand voltage of the transistor, it is necessary to adjust the concentration on the n-type diffusion layer 32, which establishes the withstand voltage. For this reason, when the above-noted high withstand voltage diode is formed on the same chip for the purpose of protecting a high-voltage transistor on that chip, there is the problem that it is necessary to form separately an n-type diffusion layer 32 for a high withstand voltage diode and an n-type diffusion layer for a transistor, these diffusion layers having different concentrations, which results in an increase in the number of manufacturing steps, and an increase in cost.
FIG. 4(b) shows the example of shorting a gate electrode 47 and a source electrode 49 of a high-voltage transistor and using the high-voltage transistor as a protective diode.
In this drawing, the reference numeral 42 denotes an n-type diffusion layer that is formed on a p-type substrate 41, 43 is a low-concentration p-type diffusion layer that is formed so as to be adjacent to the n-type diffusion layer 42, 44 is a high-concentration p-type diffusion layer that is formed on the surface of the low-concentration p-type diffusion layer 43, 50 is a high-concentration n-type diffusion layer that is formed on the surface of the low-concentration p-type diffusion layer 43, 45 is a high-concentration n-type diffusion layer that is formed on the surface of the n-type diffusion layer 42, 47 is a gate electrode, which is formed via a gate oxide film so as to straddle the low-concentration p-type diffusion layer 43 and the n-type diffusion layer 42, the gate electrode 47 is electrically connected to the high-concentration n-type diffusion layer 50, 48 is a drain electrode that is formed on the high-concentration n-type diffusion layer 45, 49 is a source electrode that is formed on the high-concentration p-type diffusion layer 44 and the high-concentration n-type diffusion layer 50, and 46 is a field oxide film.
In the case of the structure shown in FIG. 4(b), however, because the withstand voltages of the protected transistor and the diode are the same, rather than allowing surge currents and the like to escape via the diode, such surge currents and the like are caused to flow in parallel through the protected transistor and the protective diode, so that the surge current flowing through the transistor is reduced, thereby improving the immunity with respect to damage from surges.
For this reason, a larger protective diode is required, this resulting in an increase in the cost of the chip. With the diode shown in FIG. 4(b), a parasitic NPN transistor is formed by the n-type diffusion layer 42, the p-type diffusion layer 43, and the n-type diffusion layer 50 that are formed between the anode and the cathode.
For this reason, when the parasitic NPN transistor is turned on, because of the current concentration and breakdown resulting, the current immunity of this diode after a breakdown was worse than that of a P-N junction alone.
Accordingly, it is an object of the present invention to improve on the above-noted drawbacks of the prior art, by providing a high withstand voltage diode, in which, without an increase in the number of manufacturing process steps, a high withstand voltage diode is formed that has a lower withstand voltage that the high-voltage transistor to be protected, thereby reliably protecting the high-voltage transistor. It is a further object of the present invention to provide a method for manufacturing the above-noted high withstand voltage diode.
To achieve the above-noted object, the present invention has the following basic technical constitution.
Specifically, the first aspect of a high withstand voltage diode according to the present invention is a high withstand voltage diode formed on a semiconductor substrate of a first conductivity type comprising, a first region of a second conductivity type formed on the semiconductor substrate, a high-concentration second region of the second conductivity type formed on a surface of the first region,a cathode electrode that is formed on the second region, a third region of the first conductivity type formed so as to be adjacent to the first region, a high-concentration fourth region of the first conductivity type that is formed on a surface of the third region, an anode electrode that is formed on the fourth region, and a gate electrode that is provided on a surface of the semiconductor substrate via an intervening gate oxide film so as to straddle the first region and the third region, the gate electrode is electrically connected to the fourth region.
The second aspect of a high withstand voltage diode according to the present invention is a high withstand voltage diode that protects a high withstand voltage transistor formed on a semiconductor substrate of a first conductivity type having a first region of a second conductivity type formed on the semiconductor substrate, a high-concentration second region of the second conductivity type formed on a surface of the first region, a drain electrode formed on the second region, a third region of the first conductivity type formed so as to be adjacent to the first region, a high-concentration fourth region of the first conductivity type formed on a surface of the third region, a high-concentration fifth region of the second conductivity type formed on a surface of the third region, a source electrode that is formed at least on the fifth region; and a gate electrode that is provided via an intervening gate oxide film so as to straddle the first region and the third region, the gate electrode being electrically connected to the fifth region, wherein the diode and the transistor are formed on a same semiconductor substrate, and the diode comprising, a first region of the second conductivity type of this diode that is formed simultaneously with the first region of the high-voltage transistor formed on the semiconductor substrate, a high-concentration second region of the second conductivity type that is formed within the first region of the diode, the high-concentration second region of the diode being formed simultaneously with said high-concentration second region of the high withstand voltage transistor, a third region of the first conductivity type that is formed simultaneously with the third region of the high withstand voltage transistor, the third region of the diode being formed so as to be adjacent to said first region of said diode, a cathode electrode formed on the second region of the diode, a high-concentration fourth region of the first conductivity type that is formed within the third region of the diode, the high-concentration fourth region of the diode being formed simultaneously with the high-concentration fourth region of the high withstand voltage transistor, and an anode electrode formed on the fourth region of said diode, a gate electrode that is provided on a surface of the semiconductor substrate via an intervening gate oxide film so as to straddle the first region and the third region of the diode, the gate electrode being electrically connected to the fourth region of said diode.
In the third aspect of a high withstand voltage diode according to the present invention, a distance from an edge of the first region to an edge of the second region of the diode is smaller than that of the transistor.
In the fourth aspect of a high withstand voltage diode according to the present invention, the high withstand voltage diode is formed on an SOI substrate.
The first aspect of a method according to the present invention is a method of manufacturing a high withstand voltage diode formed on a semiconductor substrate of a first conductivity type having a first region of a second conductivity type formed on the semiconductor substrate, a high-concentration second region of the second conductivity type formed on a surface of the first region, a cathode electrode that is formed on the second region, a third region of the first conductivity type formed so as to be adjacent to the first region, a high-concentration fourth region of the first conductivity type that is formed on a surface of the third region, an anode electrode that is formed on the fourth region, and a gate electrode that is provided on a surface of the semiconductor substrate via an intervening gate oxide film so as to straddle the first region and the third region, the gate electrode being electrically connected to said fourth region, wherein a distance from an edge of the first region to an edge of the second region of the diode is made a prescribed length, so as to adjust the withstand voltage.
The second aspect of a method according to the present invention is a method for manufacturing a high withstand voltage diode that protects a high withstand voltage transistor formed on a semiconductor substrate of a first conductivity type having a first region of a second conductivity type formed on the semiconductor substrate, a high-concentration second region of the second conductivity type formed on a surface of the first region, a drain electrode formed on the second region, a third region of the first conductivity type formed so as to be adjacent to the first region, a high-concentration fourth region of the first conductivity type formed on a surface of the third region, a high-concentration fifth region of the second conductivity type formed on a surface of the third region, a source electrode formed at least on the fifth region; and a gate electrode that is provided on a surface of the substrate via an intervening gate oxide film so as to straddle the first region and the third region, the gate electrode being electrically connected to the fifth region, wherein the diode having a first region of a second conductivity type formed on the semiconductor substrate of a first conductivity type, a high-concentration second region of the second conductivity type formed on a surface of the first region, a cathode electrode that is formed on the second region, a third region of the first conductivity type formed so as to be adjacent to the first region, a high-concentration fourth region of the first conductivity type that is formed on a surface of the third region, an anode electrode that is formed on the fourth region, and a gate electrode that is provided on a surface of the semiconductor substrate via an intervening gate oxide film so as to straddle the first region and the third region, the gate electrode being electrically connected to the fourth region, wherein the diode and transistor are formed on a same semiconductor substrate, and the first region of the transistor and the first region of the diode, the third region of the transistor and the third region of the diode, and the second region of the transistor and the second region of said diode are respectively formed simultaneously.
In the third aspect of a method of manufacturing a high withstand voltage diode according to the present invention, the high withstand voltage diode is formed on an SOI substrate.
In a high withstand voltage diode configured as described above, it is possible to adjust the withstand voltage by making the length from an edge of the second region to an edge of the third region a prescribed length, thereby making it possible to manufacture a high withstand voltage diode having a withstand voltage that is smaller than the withstand voltage of the transistor that is being protected.